Genes controlling terminal differentiation are one class suppressor genes. In order to identify genes associated with the terminal differentiation of epithelial cells, two CDNA libraries are being constructed. The first library is from R.1 cells which do not differentiate in response to serum or transforming growth factor (TGF)-beta. The second is from S.6 cells treated with TGF-beta, which induces their differentiation. To investigate differences in gene expression in these cells, a subtractive hybridization approach will be taken. Briefly, in vitro synthesized RNA from one library and cDNA from the other library will be hybridized to subtract out common messages, and unique single-stranded messages will be subcloned to make a third, "subtracted" library. The clones from the subtracted library can then be tested for their ability to induce differentiation and/or to suppress tumorigenicity in normal or neoplastic human bronchial epithelial cell lines.